FIG. 15 is a cross-sectional view showing a thin-film structural body 101 formed by using a conventional manufacturing method of a thin-film structural body. The thin-film structural body 101 is provided with a supporting portion 103 and a floating portion 105 supported by the supporting portion 103, and is formed above a substrate 107 by using a conductive material. The floating portion 105, which is placed with a predetermined distance from the substrate 107, extends outwards from the upper portion of the supporting portion 103.
The substrate 107 is provided with a substrate main body 111, a first insulating film 113, a wiring 115 and a second insulating film 117. The first insulating film 113 is formed on the substrate main body 111. The wiring 115 is provided on the surface of the first insulating film 113, and the surface of the first insulating film 113 and the surface of the wiring 115 are substantially flattened without a step portion. The second insulating film 117 covers the surfaces of the wiring 115 and the first insulating film 113 and side faces thereof. Here, the second insulating film 117 has a hole section 117a which opens on the surface of the wiring 115 so that the surface of the wiring 115 is selectively exposed. The supporting portion 103 is formed on the wiring 115 through the hole section 117a. 
FIGS. 10 to 14 are cross-sectional views showing a sequence of conventional manufacturing steps of a thin-film structural body. First, a substrate 107 is set. In this stage, the second insulating film 117 has no hole section 117a on the substrate 107. As shown in FIG. 11, the hole section 117a is opened in the second insulating film 117 so that the surface of the wiring 115 is selectively exposed.
Next, a sacrifice film 121 is formed on the surface of the wiring 115 thus selectively exposed and the second insulating film 117. In this manner, a structure shown in FIG. 12 is obtained. Further, a dry etching process is carried out from the surface side of the sacrifice film 121 so that an opening 121a is opened in the sacrifice film 121 and the hole section 117a is opened in the second insulating film 117; thus, an anchor hole 122 is formed so that the surface of the wiring 115 is selectively exposed. Consequently, a structure shown in FIG. 13 is obtained.
Next, as shown in FIG. 14, a thin-film layer 123 is formed on the sacrifice film 121 and the substrate 107 exposed through the anchor hole 122 by using a conductive material.
Thereafter, the thin-film layer 123 is selectively removed so that residual portions of the thin-film layer 123 form a thin-film structural body 101. Successively, the sacrifice film 121 is removed so that a structure shown in FIG. 15 is obtained. Among the residual portions of the thin-film layer 123, the portion fitted into the anchor hole 122 forms the supporting portion 103 and the portion positioned on the sacrifice film 121 forms the floating portion 105.
In the above described conventional manufacturing method, the sacrifice film 121 is desirably formed by using a material which is easily removed by etching, and, for example, a silicon oxide film is employed. With respect to the substrate main body 111, a silicon substrate is employed since a semiconductor processing technique capable of performing fine manufacturing processes is applied thereto. Further, in order to easily form the first insulating film 113 on the silicon substrate, a silicon oxide film is also employed for the first insulating film 113 in the same manner as the sacrifice film 121.
In order to prevent the first insulating film 113 from being also etched upon etching the sacrifice film 121, a material which is less susceptible to etching for the silicon oxide film, and easily processed, such as a silicon nitride film, is employed to form the second insulating film 117.
However, since a dry etching process is carried out so as to form the anchor hole 122, there is a possibility that, when the position of dry etching is offset, the second insulating film 117 fails to sufficiently cover the first insulating film 113. FIG. 16 is a cross-sectional view showing a state where, after the anchor hole 122 has been opened in an offset manner to the left side in the figure, the thin-film layer 123 is formed and this thin-film layer 123 is further patterned. The positional offset of the anchor hole 122 causes the second insulating film 117 to be removed above the wiring 115 at position Q. Consequently, there is a possibility that, at position Q, the second insulating film 117 fails to cover the first insulating film 113.
With respect to the structure shown in FIG. 16, when an etching process is carried out on the sacrifice film 121, the etchant used therein might invade between the thin-film layer 123 filled in the anchor hole 122 and the second insulating film 117 to further reach the first insulating film 113. In particular, when a silicon nitride film is used to form the second insulating film 117, the residual stress is exerted in the stretching direction with the result that the second insulating film 117 easily separates from the side faces of the wiring 115. This separation causes a higher possibility of the etchant for use in the sacrifice film 121 reaching the first insulating film 113 to etc the first insulating film 113.
In order to solve these problems, a method for making the dimension of the anchor hole 122 smaller that that of the wiring 115 so as to provide a greater margin with respect to the positional offset has been proposed. However, the reduced dimension of the anchor hole 122 causes the contact resistance between the thin-film layer 123 filled therein and the wiring 115 to increase, resulting in adverse effects from the viewpoint of electrical characteristics.
Moreover, when the dry etching process for exposing the wiring 115 is carried out, corners 122a are formed on the sacrifice film 121. The corners 122a are generated more conspicuously as the anisotropy of dry etching used for forming the anchor hole 122 becomes higher. Thus, as shown in FIG. 14, the thin film layer 123 which is filled into the anchor hole 122, and covers the sacrifice film 121 is formed. Therefore, as shown in FIG. 15, in the thin-film structural body 101, internal angles 131 are formed between the supporting portion 103 and the floating portion 105. Stresses are concentrated onto each internal angle 131, resulting in a higher possibility of reduction in the strength of the thin-film structural body 101.